In order to drive on snowy and icy roads, studded tires and chains to be wrapped around tires were used. They, however, cause environmental issues such as dust pollution. Therefore, studless winter tires have been developed as alternative tires for snowy and icy roads. Studless winter tires, which are used on snowy and icy roads having higher surface roughness than normal roads, have improved in materials and designs. For example, proposed is a rubber composition containing a diene rubber that is excellent in low-temperature characteristics, and an increased amount of a softener for enhancing a softening effect. The softener generally used is mineral oil because it enhances low-temperature characteristics.
An increased amount of mineral oil for improving low-temperature characteristics, however, usually deteriorates abrasion resistance. One of measures to solve this problem is replacing mineral oil with aromatic oil. However, this method reduces low-temperature characteristics, and thus sufficient performance on ice and snow is difficult to achieve. Meanwhile, using aromatic oil together with silica can improve low-temperature characteristics without reducing abrasion resistance. The resulting properties, however, are still at insufficient levels. Moreover, improved wet grip performance is also desired in addition to improvements in low-temperature characteristics and abrasion resistance.
For example, Patent Literature 1 discloses a rubber composition for studless winter tires, which contains large amounts of aromatic oil and silica and thereby achieves a balanced improvement in abrasion resistance, performance on ice and snow, and wet grip performance. However, further improvements in these properties have recently become required.